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> For exposure purposes, f1.5 is the accurate and most important spec for that lens. This is a very common misunderstanding. To whatever extent the camera "loo

by wyager 3y ago

> For exposure purposes, f1.5 is the accurate and most important spec for that lens. This is a very common misunderstanding. To whatever extent the camera "looks like" it's using a 35mm-format f/1.5 lens from an exposure standpoint, it's only because the sensor gain is turned way up to compensate. As a result, SNR is worse, so it's like you took a darker exposure on a better camera and then cranked it up in post.

oktoberpaard 3y ago
At a given shutter speed, the sensor gain is exactly as high as you would expect it to be at f/1.5. It’s just that with the much smaller surface area of the sensor, the signal-to-noise ratio is way worse.
- wyager 3y ago
  The only invariant way of specifying gain is ADC linear brightness units per incident photon per subtended angle, in which case the iPhone's gain is vastly higher.
  - musictubes 3y ago
    Sensor speed is a completely irrelevant spec when it comes to maximum f-stop of a lens. The f-stop is a physical ratio. People that try to make "equivalent" f-stops do so by throwing out what it actually means in order to gauge some arbitrary level of performance of a format that fewer and fewer people know anything about. All of this nonsense started with digital photography. There was close to a century of shooting with different formats and lenses without ever trying to twist what an f-stop meant. Open up an ASC handbook and you'll find DOF charts for different formats and lenses but no talk of equivalent anything. I want to know the actual specs of a lens, that is how you can compare with similar systems. I wish Apple would drop the now irrelevant references to 35mm. I also wish people would stop confusing a physical measurement with a quality target. To reiterate, I find the concept of equivalent f-stops to be nonsensical and think they only confuse the issue.
    - wyager 3y ago
      > The f-stop is a physical ratio. Which tells you precisely nothing at all without having other specs to multiply it out. It's a useless spec, in the format presented by Apple. > gauge some arbitrary level of performance The fact that it's arbitrary is irrelevant; the important part is that it is a consistent reference point across cameras. > I wish Apple would drop the now irrelevant references to 35mm. Yes, that would be ideal, but they're not going to do that, so at the very least they should just be consistent with the specs they provide.
musictubes 3y ago
Again, trying to normalize on what things look like when shot with a 35mm sensor is irrelevant. If you have two camera phones with similar sized sensors and focal lengths, an f1.5 lens is almost a full stop faster than an f2 lens. Yes, the resultant SNR is worse on a small sensor but fstops are a ratio of focal length to aperture size not a measure of DOF or SNR. The f1.5 lens will have narrower DOF and let in more light. F1.5 is an accurate way of marketing the lens. Like I said before, trying to normalize different aspects of images and the resultant quality by trying to make f-stops something they aren't only confuses and obscures what is actually happening and prevents sensible discussions of camera systems. The 35mm equivalent focal length is used just to give an idea about FOV. I wish they would just give us the angle of view in degrees instead. Then maybe people would stop trying to mangle what fstops means in regards to DOF, the amount of light the sensor sees, SNR etc. Compare similar sensor systems, stop trying to cram one into the other.
- wyager 3y ago
  > fstops are a ratio of focal length to aperture size This number in isolation is completely useless for telling anything about how the resultant image is going to look. As opposed to, say, equivalent focal length, which tells you valuable information (about FoV) independently of any other spec. > I wish they would just give us the angle of view in degrees instead I agree, it would be nice if they just used invariant specs for everything. FoV angle and linear aperture diameter would be sufficient for most use cases.

by wyager 3y ago

oktoberpaard 3y ago

At a given shutter speed, the sensor gain is exactly as high as you would expect it to be at f/1.5. It’s just that with the much smaller surface area of the sensor, the signal-to-noise ratio is way worse.

wyager 3y ago
The only invariant way of specifying gain is ADC linear brightness units per incident photon per subtended angle, in which case the iPhone's gain is vastly higher.
- musictubes 3y ago
  Sensor speed is a completely irrelevant spec when it comes to maximum f-stop of a lens. The f-stop is a physical ratio. People that try to make "equivalent" f-stops do so by throwing out what it actually means in order to gauge some arbitrary level of performance of a format that fewer and fewer people know anything about. All of this nonsense started with digital photography. There was close to a century of shooting with different formats and lenses without ever trying to twist what an f-stop meant. Open up an ASC handbook and you'll find DOF charts for different formats and lenses but no talk of equivalent anything. I want to know the actual specs of a lens, that is how you can compare with similar systems. I wish Apple would drop the now irrelevant references to 35mm. I also wish people would stop confusing a physical measurement with a quality target. To reiterate, I find the concept of equivalent f-stops to be nonsensical and think they only confuse the issue.
  - wyager 3y ago
    > The f-stop is a physical ratio. Which tells you precisely nothing at all without having other specs to multiply it out. It's a useless spec, in the format presented by Apple. > gauge some arbitrary level of performance The fact that it's arbitrary is irrelevant; the important part is that it is a consistent reference point across cameras. > I wish Apple would drop the now irrelevant references to 35mm. Yes, that would be ideal, but they're not going to do that, so at the very least they should just be consistent with the specs they provide.

musictubes 3y ago

Again, trying to normalize on what things look like when shot with a 35mm sensor is irrelevant. If you have two camera phones with similar sized sensors and focal lengths, an f1.5 lens is almost a full stop faster than an f2 lens. Yes, the resultant SNR is worse on a small sensor but fstops are a ratio of focal length to aperture size not a measure of DOF or SNR. The f1.5 lens will have narrower DOF and let in more light. F1.5 is an accurate way of marketing the lens. Like I said before, trying to normalize different aspects of images and the resultant quality by trying to make f-stops something they aren't only confuses and obscures what is actually happening and prevents sensible discussions of camera systems. The 35mm equivalent focal length is used just to give an idea about FOV. I wish they would just give us the angle of view in degrees instead. Then maybe people would stop trying to mangle what fstops means in regards to DOF, the amount of light the sensor sees, SNR etc. Compare similar sensor systems, stop trying to cram one into the other.

wyager 3y ago
> fstops are a ratio of focal length to aperture size This number in isolation is completely useless for telling anything about how the resultant image is going to look. As opposed to, say, equivalent focal length, which tells you valuable information (about FoV) independently of any other spec. > I wish they would just give us the angle of view in degrees instead I agree, it would be nice if they just used invariant specs for everything. FoV angle and linear aperture diameter would be sufficient for most use cases.